Grain boundary effects on magnetotransport in bi-epitaxial films of La${}_{0.7}$Sr${}_{0.3}$MnO${}_3$

Abstract

The low field magnetotransport of La${}_{0.7}$Sr${}_{0.3}$MnO${}_3$ (LSMO) films grown on SrTiO${}_3$ substrates has been investigated. A high qualtity LSMO film exhibits anisotropic magnetoresistance (AMR) and a peak in the magnetoresistance close to the Curie temperature of LSMO. Bi-epitaxial films prepared using a seed layer of MgO and a buffer layer of CeO${}_2$ display a resistance dominated by grain boundaries. One film was prepared with seed and buffer layers intact, while a second sample was prepared as a 2D square array of grain boundaries. These films exhibit i) a low temperature tail in the low field magnetoresistance; ii) a magnetoconductance with a constant high field slope; and iii) a comparably large AMR effect. A model based on a two-step tunneling process, including spin-flip tunneling, is discussed and shown to be consistent with the experimental findings of the bi-epitaxial films.

arXiv commentREVTeX style; 14 pages, 9 figures. Figure 1 included in jpeg format (zdf1.jpg); the eps was huge. Accepted to Phys. Rev. B

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• Nonresonant microwave absorption in epitaxial La-Sr-Mn-O films and its relation to colossal magnetoresistance
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• Point contact investigations of film and interface magnetoresistance of La${}_{0.7}$Sr${}_{0.3}$MnO${}_3$ heterostructures on Nb:SrTiO${}_3$